Once again the world faces the dreadful possibility that an aggressor — this time a rogue nation widely believed to be delusional — may try to make good on its threat to attack our country with a long-range missile armed with a nuclear warhead.

North Korea may have the world’s most inscrutable political and military leadership, so when that leadership — personified by the immature and inexperienced Kim Jong Un — warns it is prepared to launch a pre-emptive nuclear strike, then the threat must be taken seriously even if it is probably just so much chest-thumping bluster.

There are valid reasons for concern. In December, North Korea launched a long-range rocket, although we were told it was designed simply to put a satellite into orbit. Months earlier, a powerful mobile missile — one that Pentagon analysts believe could reach the United States — was seen in a North Korean military parade. The fact it is mobile means it could be moved from place to place and therefore made more difficult for our side to spot.

Last week, a North Korean government agency mocked “the puppet authorities and despicable reptile media” that have criticized the continued expansion of the nation’s nuclear capabilities. Those “puppet authorities” are just across the border in South Korea, a reliable ally of the United States. The North Koreans also announced they were nullifying the joint declaration on the de-nuclearization of the Korean Peninsula that was issued after the Korean War of the 1950s.

It would be comforting to believe that North Korea is engaged in the ages-old political art of saber-rattling, but Washington and South Korea dare not take that risk. So Defense Secretary Chuck Hagel announced last week that, just in case, the United States will add additional ground-based missile interceptors on the West Coast to improve our ability to defend our shores from any attack by North Korea.

Hagel told reporters that with 14 additional interceptors in place by 2017, the total would rise to 44. In all, the Pentagon reported, it plans to spend $1 billion on improving its defense capabilities.

“The reason that we are doing what we are doing and the reason we are advancing our program here for homeland security is to not take any chances, is to stay ahead of the threat and to assure any contingency,” Hagel explained.

His remarks prompted Chinese authorities to warn Monday that his plan runs the risk of increasing tensions with North Korea.

“Bolstering missile defenses will only intensify antagonism, and it doesn’t help to solve the issue,” Hong Lei, speaking for the Chinese Ministry of Foreign Affairs, said in Beijing.

But President Obama and his advisers understand the situation clearly. In a television interview last week, the president conceded that he doubts North Korea actually has the capacity to carry out the threatened missile attack on the United States. That is, he appears to believe Kim Jong Un is bluffing.

“But we don’t like the margin of error,” he added, and most Americans — regardless of political affiliation — probably feel the same way.

Therefore the deployment of the extra missiles appears to be the only sensible path for the United States to take.